The present invention relates to a transmission used for various machines requiring the transmission of power, such as automobiles, bicycles, and other transportation machines.
Conventionally, there has been known a transmission comprising an endless belt passing around a pulley, in which a belt winding portion of the pulley is formed by many movable members arranged at intervals in the circumferential direction, and the movable members are moved in the radial direction, by which the diameter of the belt winding portion of the pulley is changed, as disclosed in Japanese Patent Laid-Open No. 62-75167, for example.
However, like the above-described transmission, a construction which transmits power by means of belt-to-pulley contact has a problem in that the whole transmission is made large when great power is transmitted because the transmission efficiency of power is decreased by a slip of the belt, so that it is difficult to practically use such a construction.
To solve this problem, for example, International Publication No. WO93/07045, U.S. Pat. No. 5,049,113, and German Patent No. 727593 have disclosed a transmission comprising a winding member with ends which are wound around the movable members of the pulley from the outside, wherein one end of the winding member is fixed to a predetermined movable member, the other end of the winding member is inserted into the inside of the pulley in an unfixed state, and a transmitting member comprising a toothed belt or a chain is engaged with the winding member. This configuration has an advantage that a slip does not occur when power is transmitted because the transmitting member is engaged with the winding member. However, in such a configuration, because bending points of the winding member and bending points of the transmitting member (for example, turning support points connecting components of the chain) are away from each other in the radial or circumferential direction of the pulley, the winding member and the transmitting member are engaged with each other when the pulley has a predetermined diameter, but when the diameter of the pulley changes, the positions of the bending points of the winding member and the bending points of the transmitting member shift in the circumferential direction of the pulley, so that the winding member and the transmitting member cannot be engaged with each other. Therefore, it is impossible to practically use the conventional construction as a transmission.
The present invention has been made to solve the above problems, and accordingly an object thereof is to provide a transmission capable of surely transmitting power even in a configuration in which the diameter of a rotating body is changed.
To attain the above object, the present invention provides a transmission comprising an endless transmitting member having many engagement portions arranged at equal intervals in the peripheral direction on the inner peripheral surface thereof and a pair of rotating bodies around which the transmitting member passes, wherein the transmitting member winding portion of at least one rotating body is formed by many movable members which are arranged at intervals in the circumferential direction of the rotating body and capable of moving in the radial direction of the rotating body, and the diameter of the winding portion of the rotating body is increased or decreased by moving the movable members in the radial direction, characterized in that there is provided a winding member with ends which is wound around the winding portion of the rotating body from the outside, one end of which is fixed to a predetermined movable member, the other end side of which is inserted into the inside of the winding portion through between predetermined movable members, and which has many engagement portions engaging with engagement portions of the transmitting member on the outer peripheral surface; the movable members are provided so as to move stepwise in the radial direction of the rotating body so that the circumferential length of the winding member at the winding portion changes in increments of the predetermined number of the engagement portions; and when the winding member and the transmitting member are engaged with each other, bending points thereof come to almost the same positions. Thereby, a rotational force is transmitted by the engagement of the engagement portions of the transmitting member with the engagement portions of the winding member, so that power is transmitted without the occurrence of a slip between the transmitting member and the winding member. Therefore, the power transmitting efficiency can be enhanced, and the transmission body can be made small. Also, when the movable members are moved in the radial direction, the diameter of the winding member that is wound around the movable members increases or decreases, so that the speed reducing ratio with respect to the other rotating body changes. That is to say, the circumferential length of the winding member that is wound around the movable members is changed by causing the other end side of the winding member to go in or out through between the movable members. At this time, the circumferential length of the winding member changes stepwise by the predetermined number of the engagement portions of the winding member, so that the engagement portions of the transmitting member and the winding member are always engaged surely with each other at any speed change position. At this time, when the winding member and the transmitting member are engaged with each other, the bending points thereof come to almost the same position, so that the positions of the bending points of the winding member and the transmitting member do not change relatively even if the diameter of the winding portion of the rotating body is changed. Therefore, even if the diameter of the rotating body is changed, the engagement state of the winding member with the transmitting member can be kept surely.
Also, according to the present invention, in the above configuration the rotating body comprises a first side plate rotating integrally with the rotating shaft of the rotating body, and a second side plate capable of turning relative to the first side plate around the rotating shaft of the rotating body; the first side plate is formed with many elongated holes engaging movably with the movable member; and the second side plate is formed with many elongated holes engaging movably with the movable member and intersecting the elongated hole in the first side plate. Thereby, by relatively turning the first and second side plates, the diameter of the winding member that is wound around the movable members is changed. Therefore, a reliable speed change operation can be provided by a simple structure, which is very advantageous in practical use. In this case, the elongated holes of the first side plate are formed straight in the radial direction, and the elongated holes of the second side plate are formed slantwise with respect to the elongated hole in the first side plate. Thereby, when the movable members are moved in the radial direction, a relative rotational difference between the movable members and the rotating body does not occur. Therefore, the tension of the transmitting member does not change at the time of speed change, and a stable speed change operation can always be performed.
Also, according to the present invention, in the above configuration, a plurality of winding members are provided in the circumferential direction or the width direction of the rotating body, and the winding members are arranged so as to be symmetrical with each other with respect to the rotating shaft of the rotating body. Thereby, the center of gravity of the rotating body can always be maintained on the rotating shaft thereof, and vibrations caused by a positional shift between the center of rotation and the center of gravity of the rotating body can surely be prevented from occurring.
Also, according to the present invention, in the above configuration, on one end side in the axial direction of the rotating body, there is provided an auxiliary member with ends which has a mass and a length equivalent to those of the winding member and moves in the radial direction of the rotating body in synchronism with the winding member, and the auxiliary member is arranged so as to be symmetrical with the winding member with respect to the rotating shaft of the rotating body. Thereby, the center of gravity is displaced with respect to the rotating shaft of the rotating body by the other end side of the winding member in an unfixed state existing partially in the circumferential direction. However, the auxiliary member having a mass and a length equivalent to those of the winding member is arranged so as to be symmetrical with the winding member, and moves in the radial direction of the rotating body in synchronism with the winding member, so that the displacement of the center of gravity of the rotating body is corrected to the side of the rotating shaft thereof, and vibrations caused by a positional shift between the center of rotation and the center of gravity of the rotating body can surely be prevented from occurring even when one winding member is used.
Also, according to the present invention, in the above configuration, the transmitting member is formed by many link members both ends of which are connected to each other rotatably, the engagement portions are formed with the turning support point of the link member being the center, and a concave portion for accommodating a portion between the engagement portions in the winding member is provided between the turning support points of the link member. In this case, the link member is formed so that a part of the concave portion extends to a portion beyond a straight line connecting the turning support points of the link member. Thereby, when a tensile force is applied to the transmitting member, the link member is subjected to elastic bending deformation. Therefore, if a sudden driving force is applied to the transmitting member, the shock can be absorbed, and the reduction in noise and the improvement in durability can be achieved.